Turbine with adjustable stator blades



Oct. 15, 1957 J. FEATONBY 2,809,803

' TURBINE WITH ADJUSTABLE STATOR BLADES Original Filed April iio. 1951By/M+% M/ Arron/v r5.-

TURBINE WITH ADJUSTABLE STATOR BLADES Joseph Featonby, Ottawa, Ontario,Canada, assignor to National Research Council, Ottawa, Ontario, Canada,a body corporate Original application April 30, 1951, Serial No.223,673, now Patent No. 2,697,326, dated December 21, 1954. Divided andthis application November 15, 1954, Serial No. 468,955

2 Claims. (Cl. 253-78) This application is a division of United Statesapplication Serial No. 223,673, filed April 30, 1951, now Patent No.2,697,326.

This invention relates generally to turbines, and more particularly tomeans for varying the angles of attack of rotor blading. Where theangles of attack of the stator blades are variable, the probability ofreaching the choking point in, say, a high compression ratio turbinewould be greatly reduced and blow oil in starting may be obviated.

Despite these attractive possibilities, it is still normal practice todesign turbines with the angle of attack of the stator blades fixed,since no simple practical means has been provided for varying the nozzleopenings according to load. I am well aware that there have been manyproposals for accomplishing this desirable variation of the blades, butnone of the prior proposals known to me have been sufficiently simpleand eifective to lead to any wide acceptance.

The basic principle underlying my invention is the adjustment of theangles of attack of stator blades of a turbine by means of a simplemechanical arrangement which is directly actuated in a positive mannerby the radial thermal growth of the turbine, a factor which haspreviously been regarded only as a handicap in turbine design.

It is interesting to note that, while as pointed out above, it has beenknown for years that it would be advantageous to be able to vary thenozzle openings, it is today common practice to use non-adjustablestator blades and to give the leading edges of the rotor blades agreater thickness than the optimum for efficiency in order that thereactor may give a reasonable performance off the design point. Withthis compromise, when the turbine is running oi the design point, therotor blades offer a better angle of reception to the gases flowing fromthe turbine nozzles, but the efficiency of the turbine at its designpoint is reduced due to the increased thickness of the leading edges ofthe rotor blades and the consequent reduction of the area for passage ofthe gases. The relative Mach number is increased and may becomecritical. That this unsatisfactory compromise is tolerated, is, I feel,evidence that the prior proposals for varying the angles of attack ofstator blades are either inoperative or complicated to the point ofimpracticability.

My simple proposal for utilizing the radial thermal growth of theturbine components to vary the nozzle openings with temperature permitsrotor blade design which offers an efficient reception angle to thegases flow- United States Patent ing to the rotor blades from theadjustable stator blades. Improved performance, both at and oil thedesign point, results from my proposal.

My invention may generally be defined as the provision, in a turbinehaving an outer stator casing, an inner stator casing, and a pluralityof adjustable stator blades mounted between inner and outer statorcasings, of means for varying the angles of attack of the adjustablestator blades, said means comprising means for mounting each of theadjustable blades to rotate about an axis which is fixed with respect tothe stator casing, a member surrounding the outer stator casing andspaced therefrom so as to be relatively unaffected by heat developedduring operation of said rotor, and a linkage connecting said member andeach blade, each linkage consisting of an element extending radiallybetween a blade and said member, projections extending transversely fromsaid radially extending element, a sleeve extending radially over aportion of the distance said member is spaced from the outer statorcasing, and arcuate guide slots extending in a gen-' erally radialdirection in the inner side walls of said sleeve, said projectionsriding in said arcuate guide slots, said guide slotsbeing arranged toimpart rotary motion to said blades whenever radial thermal growth ofsaid turbine causes relative radial movement of said member and saidstator casing and thus forces sliding of said projections in saidarcuate slots.

In drawings which illustrate a presently preferred embodiment of theinvention applied to turbines:

Figure l is a side elevation, partly broken away, of said embodiment;

Figure 2 is a fragmentary section on an enlarged scale showing the meansfor adjustably mounting one of the blades;

Figure 3 is a section on the line 3-3 of Figure 2, with the outer statorcasing removed to render the blade visible, and

Figure 4 is a detail of one of the blade-adjusting slots.

Referring first to Figures 1 and 2, reference numeral ll indicates thewall of the combustion chamber of a gas turbine, 11 indicates the outerstator casing, "and 12 the inner stator casing. A plurality of statorblades, one of which is indicated at 13, extend between the two statorcasings andare each mounted to rotate about an axis which is fixed withrespect to the stator casing. A circular flange 14 extends around thecombustion chamber at the end adjacent the stator, the flange beingrigidly secured to the combustion chamber wall 10. An expansion joint 15is provided between flange 14 and the forward end of outer stator casing11. A tubular member 25 is generally concentrically disposed withrespect to the stator casing, being spaced some distance outwardlytherefrom and enveloping the outer casing 11 in the region of theadjustable blades 13. Tubular member 25 is rigidly secured to a portionof the apparatus which is relatively unafiected by the heat developedduring operation of the turbine. For example it might be attached to theengine nacelle of an aeroengine or to the bedplate of a stationaryturbine.

Each blade 13 is mounted for roation within the stator casing by acylindrical boss 16 disposed within a cylindrical recess in casing 12and .a cylindrical boss 17 which is received in a cylindrical recess inouter casing 11. Bosses 1'6 and 17 are preferably integral with theblade 13, but are in any event fixed with respect thereto. A rod-likemember 18 projects axially from, and is rigidly secured to (or isintegral with), boss 17, and extends through casing 11, projectingtherewithout. A collar is fixed to rod-like member 18 where the latteremerges from stator casing 11; and two diametrically opposed transverseprojections 20 extend from rod-like member 18 adjacent the free endthereof.

V A plurality of sleeves 21 are mounted on the tubular member 25, andlike member 25 are relatively unaffected by the heat developed duringoperation of the turbine. Two similar but diametrically opposed guideslots 22 are provided in the; inner side wall of each sleeve 211. SlotsWhile extending generally radially, are arcuate over a portion of theirlengths so that they are partially axially directed. The slots areslightly wider than the diameter of the projections 26. The free end ofeach rod-like member 18 is disposed within one of the sleeves 21, withthe projections 29 riding in the guide slots 22. Sleeves 21 are splinedor keyed to the tubular member 25 as indicated at 23, whereby relativemovement, axially of the turbine, is permitted between the sleeves 21and the member 25, although no relative radial movement is permitted.

The angles of attack of adjustable blades 13 will be varied inaccordance with the temperature of the motive gases in the followingmanner. The hot gases passing through the turbine cause turbine casings1i and 12 to expand. Member 25 and sleeves 231 will be relativelyunaffected by the heat developed and will remain at a relatively fixedradial distance from the longitudinal axis of the stator casing. Radialoutward expansion of outer stator casing 11 moves collar 19 outwardly,and rod-like members 18 are carried further into the sleeves 21. As themembers 18 penetrate sleeves 21 more deeply the projections 2% areforced to slide in the arcuate slots 22, and the curvature of the slotsforces the rod-like members 18 to rotate. Rotation of the members 18 inturn rotates the blades 13.

Since the outer stator casing 11 will expand and contract in advance ofthe inner casing 12, I recommend that a clearance as indicated at 24, beleft between each blade 13 and the inner stator casing 12 to avoiddamage of the blade. I should also like to point to the advisability. ofleaving adequate clearance between the rod-like members 18 and thesleeves 21 on the one hand, and between projections 20 and slots 22 onthe other hand,

since otherwise binding may occur due to the fact that member 13 and theprojections 20 are more affected by heat than the sleeves 21 and theirslots 22.

What I claim as my invention is:

1. A turbine having an outer stator casing, an inner stator casing, anda plurality of adjustable stator blades mounted in and extending betweensaid inner and outer stator casings, said blades being mounted in saidstator casings for rotation about axes which are fixed with respect tothe casings, and means. for varying the angles of attack of theadjustable stator blades, said means comprising a tubular membersurrounding the outer stator casing and spaced therefrom so as to berelatively unaffected by heat developed during operation of saidturbine, and a linkage connecting said tubular member and each blade,each linkage consisting of a rod-like member fixed to one of said bladesand extending radially between said blade and said tubular member,projections fixed to said radially extending element and extendingtransversely therefrom, a sleeve extending radially over a portion ofthe distance said member is spaced from the outer stator casing, saidsleeve being radially fixed with respect to said tubular member andhaving an inner side wall, and guide slots extending in a generallyradial direction in said inner side wall, said slots being arcuate overa portion of their lengths so that they are partially axially directed,said projections riding in said guide slots, wherein rotary motion isimparted to said blades whenever radial thermal growth causes relativeradial movement of said tubular member and said stator casings and thusforces sliding of said projections in said guide slots.

2. A turbine as defined in claim 1, wherein said adjustable blades aremounted in said stator casings by means of bosses fixed to the, oppositeends of said blades and, cylindrical recesses in said inner and outerstator casings for the reception of said bosses.

No references cited.

